linux-kernel - Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu barrier

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Date:	Tue, 17 Nov 2015 16:42:49 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Noam Camus <noamc@...hip.com>, <linux-snps-arc@...ts.infradead.org>
CC:	<linux-kernel@...r.kernel.org>, <talz@...hip.com>,
	<gilf@...hip.com>, <cmetcalf@...hip.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu
 barrier

On Saturday 07 November 2015 04:22 PM, Noam Camus wrote:
> From: Tal Zilcer <talz@...hip.com>
> 
> In SMT system like we have the generic "sync" is not working with
> HW threads. The replacement is "schd.rw" instruction that is served
> as cpu barrier for HW threads.

As discussed in v2 of this patch, SYNC or some such in __switch_to is completely
superfluous. We don't need this patch, you may instead wanna submit a patch which
removes the sync. Also please do that in assembler version of this file as well !

> Signed-off-by: Noam Camus <noamc@...hip.com>
> ---
>  arch/arc/kernel/ctx_sw.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arc/kernel/ctx_sw.c b/arch/arc/kernel/ctx_sw.c
> index 92e2e82..2a2f50e 100644
> --- a/arch/arc/kernel/ctx_sw.c
> +++ b/arch/arc/kernel/ctx_sw.c
> @@ -61,7 +61,11 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
>  		"st      sp, [r24]       \n\t"
>  #endif
>  
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +		".word %5   \n\t"
> +#else
>  		"sync   \n\t"
> +#endif
>  
>  		/*
>  		 * setup _current_task with incoming tsk.
> @@ -122,6 +126,9 @@ __switch_to(struct task_struct *prev_task, struct task_struct *next_task)
>  #ifdef CONFIG_ARC_PLAT_EZNPS
>  		, "i"(CTOP_AUX_LOGIC_GLOBAL_ID)
>  #endif
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +		, "i"(CTOP_INST_SCHD_RW)
> +#endif
>  		: "blink"
>  	);
>  
> 

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